A local aggrettion of a species other than the dominant one in an associion brings about a plant society; for example, societies of Ericd etralix, of Scirpus caespitosus, of Molinia coerulea, of Carex irta, of Narthecium ossifra gum, and others may occur within i association of Calluna vulgaris.
Sagittaria sagittifolia, Scirpus lacustris, Hippuris vulgaris, Sium latifolium.
Sea-aster flourishes in the Wadden of Friesland and Groningen, the Dollart and the Zeeland estuaries, giving place nearer the shore to sandspurry (Spergularia), or sea-poa or floating meadow grass (Glyceria maritima), which grows up to the dikes, and affords pasture for cattle and sheep. Along the coast of Overysel and in the Biesbosch lake club-rush, or scirpus, is planted in considerable quantities for the hat-making industry, and common sea-wrack (Zostera marina) is found in large patches in the northern half of the Zuider Zee, where it is gathered for trade purposes during the months of June, July and August.
I, Flower of true bulrush (Scirpus lacustris).
A bunch of ' tang sani ' (lamp-wick, the pith of Eriocaulon or Scirpus) is then inserted well into the mass, and the pan slightly canted, when a rich, clear, brown fluid is thus drawn off, and filtered through ' chi mui ' (paper made from bamboo fibre).